18,201 research outputs found
On the equation of motion of compact binaries in Post-Newtonian approximation
A third post-Newtonian (3 PN) equation of motion for two spherical compact
stars in a harmonic coordinate has been derived based on the surface integral
approach and the strong field point particle limit. The strong field point
particle limit enables us to incorporate a notion of a self-gravitating regular
star into general relativity. The resulting 3 PN equation of motion is Lorentz
invariant, unambiguous, and conserves an energy of the binary orbital motion.Comment: 7 pages, no figure. Proceedings of the 5th Amaldi Conference on
Gravitational Waves, Pisa, Italy, 6-11 July 200
Atomically straight steps on vicinal Si (111) surfaces prepared by step-parallel current in the kink-up direction
We demonstrate that annealing of a vicinal Si(111) surface at about 800 C
with a direct current in the direction that ascends the kinks enhances the
formation of atomically straight step edges over micrometer lengths, while
annealing with a current in the opposite direction does not. Every straight
step edge has the same atomic configuration U(2,0), which is useful as a
template for the formation of a variety of nanostructures. A phenomenological
model based on electromigration of charged mobile atoms explains the observed
current-polarity dependent behavior.Comment: Accepted for publication in Appl. Phys. Lett. Numbers of pages and
figures are 12 and 4, respectivel
Comparison of Conditional Average Using Threshold and Template Methods for Quasi-Periodic Phenomena in Plasmas
Cu Nuclear Quadrupole Resonance Study of Site-Disorder and Chemical Pressure Effects on Y(Ba1-xSrx)2Cu4O8
We report a zero-field Cu nuclear quadrupole resonance (NQR) study on the
effects of nonmagnetic Sr substitution for high-Tc superconductors,
Y(Ba1-xSrx)2Cu4O8 (Tc=82-80 K for x=0-0.4), using a spin-echo technique. The
site-disordering and chemical pressure effects associated with doping Sr were
observed in the broadened, shifted Cu NQR spectra. Nevertheless, the site
disorder did not significantly affect the homogeneity of Cu electron spin
dynamics, in contrast to the in-plane impurity. The peak shift of Cu NQR
spectrum due to Sr was different between the chain- and the plane-Cu sites,
more remarkably than those under a hydrostatic physical pressure, suggesting
anisotropic or nonuniform local structural strains. The small decrease of Tc
due to Sr can be traced back to either a cancellation effect on Tc between the
disorder and the pressure, or an anisotropic or nonuniform chemical pressure
effect on Tc.Comment: 4 pages, 5 figure
Food Webs: Experts Consuming Families of Experts
The question what determines the structure of natural food webs has been
listed among the nine most important unanswered questions in ecology. It arises
naturally from many problems related to ecosystem stability and resilience. The
traditional view is that population-dynamical stability is crucial for
understanding the observed structures. But phylogeny (evolutionary history) has
also been suggested as the dominant mechanism. Here we show that observed
topological features of predatory food webs can be reproduced to unprecedented
accuracy by a mechanism taking into account only phylogeny, size constraints,
and the heredity of the trophically relevant traits of prey and predators. The
analysis reveals a tendency to avoid resource competition rather than apparent
competition. In food webs with many parasites this pattern is reversed.Comment: 16 pages, 3 figures, 1 table + Appendix of 36 pages, 18 figures.
movie available from http://ag.rossberg.net/matching.mp
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